An underreamer is a device used to enlarge the well bore below the casing. Currently used underreamers are long assemblies having blades or cutters which are moved into the well bore by mechanical means to enlarge the hole. The mechanisms for moving the cutter faces into the well bore have significantly impinged on interior space of the body and consequently restricted the fluid passage from the upper end of the underreamer to the lower end. Currently used underreamers have been long and heavy making them impractical to use with steerable downhole motors to simultaneously drill and underream.
An underreamer of the present invention is made up of a tubular upper body, threadedly connectable to a drill string, said tubular upper body having a lower end and an upper end each with a different internal diameter, wherein the inner diameter of the lower end is larger than the inner diameter of the upper end. It has a tubular lower body removably attached to the lower end of the tubular upper body, said tubular lower body having at least three skewed, longitudinal grooves and an interior surface defining a longitudinal bore therethrough and an annular lip within the tubular lower body which permits a flowpath having substantially the same diameter through the entire underreamer. It also provides a piston actuator having a longitudinal annular bore, at least three extensions, each having a slot formed thereon, and upper and lower portions, wherein said upper portion slideably and sealingly engages the interior surface of the lower end and wherein the lower portion slideably and sealingly engages the interior surface of tubular lower body and has a lower surface; at least three pins; at least three cutters, each having an ear formed thereon, wherein each of the cutters is pivotally attached within a corresponding one of said at least three skewed, longitudinal grooves using one of the at least three pins and wherein said ear engages the slot of a corresponding one of said at least three extensions; and at least one resilient member positioned between the lower surface of piston actuator and the annular lip of the tubular lower body, said at least one resilient member resisting downward longitudinal movement of the piston actuator assembly. The longitudinal movement of the piston actuator moves the arms into and out of engagement with the well bore and does not rely upon pins and linkages commonly found in prior art underreamers.
The present invention offsets the support mechanism of the cutter surfaces of the underreamer from the central longitudinal axis of the tool so that an unobstructed passageway through the tubular body may be provided. It is an object of the present invention to provide a shortened underreamer for use in all forms of drilling operations, including directional drilling operations and drilling programs using steerable downhole drilling motors to permit directional underreaming of formations. The present invention allows drilling and underreaming to occur in one continuous operation and saves the operator the time and expense of drilling a pilot hole then tripping into and out of the hole or reentering the well to underream the pilot hole. The shortened body length of the present invention also allows steerable underreaming while drilling in an economical package. The present invention also avoids the necessity of costly bicentered bit technologies and the inherent weaknesses of conventional underreamers. The present invention permits the simultaneous use of small and therefore cheaper bit technologies with the underreamer and also permits directional control of the underreamer and bit combination.
Most generally, the present invention consists of an apparatus formed from a tubular body having threaded connections at each end, an interior surface forming a longitudinal bore through said tubular body and an annular lip within said tubular body, and a plurality of skewed, longitudinal grooves formed in said body; a piston actuator having a lower surface, a plurality of slotted extensions and a longitudinal flow path through said piston actuator, wherein said piston actuator slideably and sealingly engages the interior surface; a plurality of arms, each of said arms having a pivot and an ear, wherein each of said plurality of arms is pivotally mounted in a corresponding one of said plurality of skewed, longitudinal grooves and wherein said ear is adjacent to said pivot and engages a corresponding one of said plurality of slotted extensions; and a plurality of resilient members, wherein each of said plurality of resilient members has a first end and a second end, is located adjacent to a corresponding one of said plurality of slotted extensions, the first end engages the lower surface of the piston actuator, and the second end engages the annular lip.